1. Field of the Invention
This invention relates to a sewing machine provided with a high brightness InGaN (indium-gallium-nitride) LED lamp for illuminating a sewing bed on which cloth to be sewn is placed.
2. Description of Related Art
There have conventionally been provided sewing machines comprising a sewing bed on which cloth to be sewn is placed, a pillar extending upward from the bed, and a sewing arm extending horizontally from an upper end of the pillar so as to be located over the bed. The arm is provided with an electric lamp for illuminating the bed from above. The lamp comprises a generally cylindrical glass tube and a filament disposed in the tube. The tube is filled with an inert gas etc. and hermetically sealed (electric lamp of sealed tube type).
In sewing, the user firstly places a piece of cloth on the bed. A sewing operation is carried out while the cloth is slid with the user""s hand in touch with it. In this case, the sewing can be performed while the bed on which the cloth is placed is illuminated by the aforesaid lamp. Furthermore, the user folds the cloth with his or her hand when sewing is started and finished. Thus, the user is sometimes charged with static electricity when the cloth is slid or folded.
The glass tube in which the filament and inert gas are accommodated has a diameter of 15 mm in the above-mentioned conventional illuminating device comprising the sealed-tube type lamp. A socket to which the lamp is mounted has a diameter of 20 mm, and the lamp has a length of 40 mm when mounted to the socket. As a result, the lamp increases the size of the illuminating device.
The inventor had a conception of the following illuminating device for the purpose of reducing the size thereof. The contemplated illuminating device included a diode converting electric current to light or LED lamp. The LED lamp necessitates no large space for an inert gas and filament which was required in the conventional lamp of the sealed-tube type, thereby reducing the size of a light source. The illuminating device can be reduced in the size and weight since the LED lamp has a diameter of 5 mm and length of 7.5 mm. Furthermore, use of the LED lamp can improve the service life of the illuminating device (maintenance-free for one hundred thousand hours) and prevent heating of the illuminating device. The service life of the LED lamp is restricted by a material of a lens provided in the lamp although the service life of an LED chip is almost infinite. In this case, the service life of the LED lamp can further be improved when a silicon resin is used as the material of the lens instead of an epoxy resin. When made from an epoxy resin, the lens is blurred by ultraviolet absorption such that a luminous efficiency of the LED lamp is reduced as compared with a silicon resin.
Elements of compound semiconductor used for the LED lamp include those of group III (B, Al, Ga, In, Tl) and those of group V (N, P, As, Sb, Bi) of the periodic table. III-V compound semiconductors used for the LED lamps include those of the high brightness type or high intensity type which are made from InGaN (indium-gallium-nitride) and emit blue light, those of other ternary alloys (AlGaP, AlGaAs, etc.) or those of quaternary alloys (AlGaInP). Electric energy is directly converted to light in these LED lamps using compound semiconductors of direct transition type. Accordingly, an amount of heat generated in these LED lamps is smaller than the aforesaid illuminating device using the tube-sealed electric lamp. However, since an LED lamp uses the p-n junction for light emission, it has a low breakdown voltage (not more than 1 kV) with respect to static electricity irrespective of voltage application or no-voltage. Consequently, an LED lamp is easy to be broken down by discharge from arms or hands of a person charged with static electricity depending on environment in which the LED lamp is disposed.
The user of the sewing machine is easy to be charged with static electricity generated as the result of contact of his or her hand or arm with the cloth. Accordingly, electric discharge due to the static electricity occurs such that electric current flows from the arm or hand of the user to the LED lamp, whereupon there is a possibility that the LED lamp may be broken. Thus, the LED lamp involves problems to be solved before it is employed as an illuminating device provided in the sewing machine. Therefore, the electric lamps of the sealed tube type have generally been used as the illuminating device provided in the sewing machine. Accordingly, a larger electric lamp than the LED lamp is generally used, and the sewing machine is increased in size since the LED lamp needs to be accommodated in the illuminating device. Furthermore, a peculiar noise caused by an inverter has also been a matter of concern in an illuminating device comprising a cold cathode fluorescence lamp.
Therefore, an object of the present invention is to provide a sewing machine in which the illuminating device accommodated in the sewing arm can be reduced in size without use of the electric lamps and which can be protected against static electricity.
The present invention provides a sewing machine comprising a sewing bed on which cloth to be sewn is placed, a pillar extending upward from the bed, a sewing arm extending horizontally from the pillar so as to be located over the bed, a high brightness LED lamp including a lens, a lamp cover provided to cover and support the LED lamp and made from a material which can transmit light emitted by the LED lamp, and a supporting member provided on the arm for supporting the lamp cover further supporting the LED lamp.
In the above-described sewing machine, the LED lamp is covered by the lamp cover and mounted on the supporting member provided on the arm. Consequently, the LED lamp can be prevented from being broken due to discharge from the user etc. charged with static electricity.
In a preferred form, the lamp cover diffuses the light emitted by the LED lamp in a plurality of directions intersecting each other. Furthermore, the lamp cover preferably has a surface including at least a part serving for light diffusion, said part being formed with an engraving which diffuses the light emitted by the LED lamp.